This application claims the priority of German Patent Document 101 07 871.4, filed Feb. 20, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a safety steering column for a motor vehicle, with a casing tube which is arranged concentrically to a steering shaft and is fastened to the vehicle body and which, in the event of an axial impact action, can be shortened, while at the same time absorbing energy, the casing tube consisting of two casing-tube parts which have different diameters and lie partially one in the other.
Axial sliding systems for steering columns are known in a wide variety of variants. They serve for giving way in the event of an accident and an impact of the vehicle occupant against the steering wheel caused thereby and, at the same time, for absorbing impact energy. Their operating principle is based on a securing member designed for a predetermined axial load on the steering column being released when the predetermined load is exceeded, so that the components connected to one another via the securing member can be pushed one into the other, with energy being absorbed at the same time.
Thus, for example, German Patent Document DE-A-1 755 874 (Corresponding GB 1206388) discloses a safety steering column for a motor vehicle, which has a casing tube with two casing tubes lying partially one in the other. The parts of the casing tube which lie one in the other are designed conically in specific regions. A number of elastic deformation rings are arranged in the interspace of equal width which is formed by these regions and which are in the form of a cone envelope. As a result of a specific initial displacement of the two casing tubes in the direction of a shortening of the safety steering column, the elastic deformation rings are prestressed radially and the two casing tubes are prestressed axially.
This known safety steering column has the disadvantage that the displacement force between the two casing-tube parts cannot be set or cannot be adapted to this specific application, without the components themselves being modified. Moreover, the force/travel profile when the casing-tube parts are pushed together is not constant, but decreases sharply over the running travel in a way which is unfavorable for the driver. In addition, between the two casing-tube parts, there is no provision for securing against a radial displacement of the casing-tube parts relative to one another.
Against this background, an object on which the present invention is based is to provide a safety steering column for a motor vehicle, with a shortenable casing tube, in which the displacement force between the two casing-tube parts can be set.
This object is achieved, according to preferred embodiments of the invention, by a safety steering column for a motor vehicle with a casing tube which is arranged concentrically to a steering shaft and is fastened to the vehicle body and which, in the event of an axial impact action, can be shortened, while at the same time absorbing energy, the casing tube comprising two casing-tube parts which have different diameters and lie partially one in the other, wherein a connecting element is arranged between the two casing-tube parts, the connecting element being fastened to one of the casing-tube parts and being pressed with a predetermined force into a groove introduced into the other casing-tube part. Accordingly, the invention is distinguished in that the safety steering column has a casing tube which is arranged concentrically to a steering shaft and is fastened to the vehicle body and which, in the event of an axial impact action, can be shortened, while at the same time absorbing energy, the casing tube consisting of two casing-tube parts which have different diameters and lie partially one in the other. According to the invention, a connecting element is arranged between the two casing-tube parts. The connecting element is fastened to one of the casing-tube parts and is pressed with a predetermined force into a groove introduced into the other casing-tube part.
By the force with which the connecting element is pressed into the groove being varied, the displacement force between the two casing-tube parts can be set, without the components themselves being modified. When a displacement force is referred to in connection with the invention, this means the force which acts on a steering wheel and during the exceeding of which the connecting element releases the connection between the two casing-tube parts and the two parts are pushed one into the other. Since the connecting element according to the invention is pressed into the groove, displacement can take place only by a frictional force between the connecting element and the groove in the casing-tube part being overcome. This serves for absorbing impact energy.
The setting of the displacement force is advantageous particularly when the steering shaft surrounded by the casing tube is likewise configured so as to be capable of being pushed into itself and is designed in such a way that it absorbs energy at the same time. To be precise, the displacement force of the casing tube can then be set individually, during the assembly process, to the measured actual value of a crash element located in the steering shafting, so that the safety steering column is designed optimally.
In addition, the displacement force of the safety steering column according to certain preferred embodiments of the invention is constant over the travel. This means that, irrespective of how far the two parts of the casing tube are pushed one into the other, the displacement force is always the same.
A further advantage of certain preferred embodiments of the invention is to be seen in that the crash system is reversible, that is to say a casing tube, once pushed together in the event of a crash, can be drawn apart again and set via the crash element.
According to certain preferred embodiments of the invention, the groove in one of the casing-tube parts and the connecting element engaging into the groove have a conical cross-sectional surface with respect to a sectional plane which is oriented perpendicularly to a longitudinal axis through the two casing-tube parts. After the connecting element has been pressed into the groove in this arrangement, a positive connection is made and there is therefore no play in the radial direction between the two casing-tube parts. This is important, because operating elements, such as, for example, in embodiments where the lever for actuating the direction indicator, are fastened to the casing-tube part pointing into the vehicle interior. The exertion of force on this lever should not act on the system of a safety steering column in such a way that, for example, one casing-tube part is displaced relative to the other. This is avoided by the freedom from radial play by virtue of the conical embodiment.
The same applies to the axial direction. In this direction, the freedom from play is ensured, up to a limit predetermined by the displacement force, by the connecting element being pressed into the groove.
According to a further feature of preferred embodiments of the invention, the connecting element is pressed into the conical groove by means of at least one screw. This is particularly advantageous because the displacement force can thereby be set or adapted in a particularly simple way via the tightening torque of the screws. Screws can also be set by hand according to the individual requirements even during assembly.
It has proved particularly advantageous according to certain preferred embodiments of the invention if the screw has a conical end which engages into a corresponding recess in the connecting element. Such a connection likewise affords the advantages during assembly, since the screw is automatically drawn via the conical shape into the corresponding recess in the connecting element, and there is no need to align the connecting element by hand in such a way that it interacts with the screw.
In certain preferred embodiments of the invention, the groove is introduced into the outer wall of the casing-tube part which has the smaller diameter. The screw engages correspondingly with its thread into a thread in the casing-tube part which has the larger diameter. Assembly becomes particularly simple as a result, since the screw is easily accessible from outside.
In order that the displacement force can be set specifically, it is advantageous for the connecting element to be a sliding piece according to certain preferred embodiments of the invention, of which at least the surface on which the two casing-tube parts slide against one another when they are pushed together has a defined roughness, so that the frictional force between the two casing-tube parts can be determined exactly after the tightening of the screw. Advantageously, the surface of the groove, that is to say its roughness, may also be coordinated with the surface of the sliding piece. Both surfaces are preferably made plane and smooth. The displacement force can thereby by set reliably.
It is also contemplated to use, the connecting element according to the invention in the case of a steering column which is designed so as to be capable of being pushed together for a crash. In this case, however, the torsional moments additionally occurring in the case of a steering column must be taken into account in the design.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.